The invention relates to an arrangement for open-end rotor spinning having a spinning rotor which has a fiber sliding surface expanding conically into a fiber collecting groove, a fiber feeding duct being directed to this fiber sliding surface which starts at an opening roller and tapers in the direction toward the fiber sliding surface. An insert projects into the spinning rotor and contains the end area of the fiber feeding duct and a yarn withdrawal nozzle, this insert being part of a cover which closes off a rotor housing which is connected to a vacuum source which takes in an air current via the fiber feeding duct.
In the case of arrangements of this type, as they are known, for example, from DE-A-32 47 411, the fiber feeding duct must have a sufficiently large cross-section up to its mouth so that, in the case of a given pressure gradient, a sufficiently large amount of air can be sucked through which permits optimum conveying of the fibers. The fibers conveyed in the fiber feeding duct must impact on the fiber sliding wall of the spinning rotor at a sufficient distance from the open end as well as from the fiber collecting groove. On the one hand, it must be avoided that the fibers are moved away over the open rotor edge with the conveying air, while, on the other hand, a sufficient path is required on the sliding surface so that the fibers can still be properly guided and stretched to the fiber collecting groove. In the case of modern rotor spinning machines, there is the tendency for the rotors to become progressively smaller so that the above-mentioned requirements lead to difficulties. On the one hand, it is necessary to supply the fibers in a very targeted way to a certain point of the fiber sliding surface of the spinning rotor, which can be realized by means of a fiber feeding duct with a small mouth. However, this small mouth results in an unacceptable reduction of the taken-in quantity of air required for the conveying. In order to solve this problem, it was proposed in an earlier commonly assigned U.S. application Ser. No. 149,175, filed Jan. 27, 1988, now abandoned, and based on German Application P 37 04 460.5, that the mouth of the fiber feeding duct be constructed to be large in circumferential direction of the spinning rotor, but that it be kept as small as possible in the direction of the height of the fiber sliding wall
It is also known (DE-A-31 20 877) to prevent as much as possible the depositing of fine dirt particles, particularly dust, in the spinning rotor. In the known construction, it is therefore provided that the fibers, as early as before they enter the spinning rotor, are separated from the conveying air current and thus also from fine particles For this purpose, in the known construction, the fiber feeding duct is opened up, before the spinning rotor is reached. In one embodiment, the fiber feeding duct is then equipped with a groove-shaped extension which extends to the sliding surface of the spinning rotor. A concentration of the impacting point of the fibers on the fiber sliding wall is not endeavored in the known construction.
An object of the invention is to develop an arrangement of the initially mentioned type such that, on the one hand, a sufficiently large amount of air can be taken in by the fiber duct, while, on the other hand, a sufficiently high precision is ensured with respect to the impacting point of the fibers on the fiber sliding surface of the spinning rotor.
This object is achieved according to preferred embodiments of the invention in that the fiber feeding duct, starting from its end that is opposite the fiber sliding surface, is opened up by means of a lateral slot so that the cross-section of the fiber feeding duct that is consequential to the taken-in amount of air is placed back in an area with a larger cross-section, and in that the end area of the fiber feeding duct is shaped as a groove, the groove base of which has a radius of no more than 2.5 mm.
By means of this construction, on the one hand, a sufficiently large amount of air is taken in, while, on the other hand, the alignment of the fiber conveyance is improved Among other things, the fibers are also pressed into the groove base by means of an air whirl rotating along with the spinning rotor. As soon as these fibers come in contact with the fiber sliding surface of the spinning rotor, they are pulled out via the groove base so that, in addition, there is a relatively strong stretching and parallelizing effect. In this case, the groove may also take over a sort of compressor function whereby the fed fibers are slightly bundled In this case, the shape of the groove does not only depend on the fiber thickness but also depends slightly on the yarn size; i.e., in the case of courser yarn sizes, a slightly larger radius may be selected for the groove base than in the case of fine yarn sizes.
In a further development of preferred embodiments of the invention, it is provided that the end area of the fiber feeding duct is developed as a groove that is V-shaped in its cross-section. As a result, a particularly precise fiber feeding to the fiber sliding wall of the spinning rotor is achieved.
In a further development of preferred embodiments of the invention, it is provided that the length of the end area of the fiber feeding duct that is developed as a groove, including the distance of the fiber feeding duct to the fiber sliding surface of the spinning rotor, corresponds approximately to the staple length of the fiber material to be processed. This ensures that, as a rule, a part of the fibers will still be located in the groove when the starting part has reached the sliding surface. The fibers are then pulled out via the groove base, whereby they are deflected and stretched.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings